1. Field of the Invention
The present invention relates to materials for arc welding, and in particular to flux composition for flux-cored wires for welding and surfacing high-strength alloyed steels with a gas-shielded process.
The invention may be used more efficiently in flux-cored wires designed for automatic and semiautomatic welding in normal, inclined and in horizontal position in a vertical plane.
2. The Prior Art
Known in the art are flux compositions for flux-cored wires which are used for welding and surfacing high-strength alloyed steels with CO.sub.2 -shielded process in all welding positions and which comprise a steel sheath filled with powdered flux forming a core thereof. There is also known a flux-cored wire having a flux core containing the following ingredients, by weight %:
______________________________________ low-carbon ferrochromium 18.7-75.0 ferromolybdenum 2.1-8.4 manganese 0.8-2.9 ferrosilicon 3.0-13.7 iron powder 69.0-0 (cf. U.S. Pat. No. 3,253,120) ______________________________________
It is a common knowledge that during welding a great amount of hydrogen dissolves at molting temperature in the weld joint metal, which lowers the resistance thereof to cracks. As the weld seam produced by welding high-strength alloyed steels is liable to cracks the hydrogen content in the weld seam metal should be kept as low as possible. Since the flux-cored wire having a core formed from the above flux composition does not prevent hydrogen from its dissolving in the weld metal the hydrogen content therein is considerable. In addition, the weld seams produced with the use of this flux-cored wire have a bead shape which lowers their fatigue strength.
The best results in welding and surfacing high-strength alloyed steels have been obtained with the use of a flux-cored wire having a core flux composed of the following ingradients, by weight %:
______________________________________ calcium fluoride 5-25 magnesium oxide 5-15 silicon dioxide 0-25 ferrosilicon 5-10 ferromanganese 2-5 ferrochromium 0-5 ferromolybdenum 0-20 nickel 0-20 alluminium magnesium powder 0-15 (cf. U.S. Pat. No. 3,424,892) ______________________________________
The weld seam produced with the use of a wire having the above core flux composition features high mechanical properties. Calcium fluoride contained in the above flux composition prevents the formation on the weld seam surface of the oxide film of the high melting-point oxides, and to some extent binds hydrogen dissolving in the weld metal, in the course of welding, to form volatile fluorides, thereby lowering hydrogen content in the weld metal. However, in the process of welding with the above flux-cored wires there takes place intensive spattering of the electrode metal, which is due to the fact that calcium fluoride contained in the above flux composition is known to be an active destabilizer of the arc.
In addition, weld seams produced with the use of flux-cored wires having the above core flux composition are of a bead shape and have coarse ripples, which lowers their fatigue strength. To remedy this disadvantage the resulting weld seam has to be machined, which is associated with additional labour consumption. It should be also noted that the weld seam thus obtained contains from 0.040 to 0.045 weight percent oxygen, and hydrogen inspite of the fact that the latter is partially bound by calcium fluoride at a rate of 4-5 cm.sup.3 per 100 g of the weld metal. Such content of gases in the weld metal lowers resistance thereof to cold cracks and its impact strength at temperatures both below and above zero.
The principal object of the invention is to provide a flux composition of flux-cored wires for welding and surfacing high-strength alloyed steels, which would improve welding properties of flux-cored wires.
Another object of the invention is to impart high mechanical properties to the weld seam metal.
Still another object of the invention is to lower oxygen and hydrogen content in the weld seam metal.
Yet another object of the invention is to improve notch impact strength of the weld seam metal at temperatures both above and below zero.
A further object of the invention is to enhance resistance of the weld seam metal both to cold and hot cracks.
Other objects and advantages of the present invention will be apparent from the specification given below.